54 research outputs found
Kinetic Modeling and Numerical Simulation as Tools to Scale Microalgae Cell Membrane Permeabilization by Means of Pulsed Electric Fields (PEF) From Lab to Pilot Plants
Pulsed Electric Fields (PEF) is a promising technology for the gentle and energy efficient disruption of microalgae cells such as Chlorella vulgaris. The technology is based on the exposure of cells to a high voltage electric field, which causes the permeabilization of the cell membrane. Due to the dependency of the effective treatment conditions on the specific design of the treatment chamber, it is difficult to compare data obtained in different chambers or at different scales, e.g., lab or pilot scale. This problem can be overcome by the help of numerical simulation since it enables the accessibility to the local treatment conditions (electric field strength, temperature, flow field) inside a treatment chamber. To date, no kinetic models for the cell membrane permeabilization of microalgae are available what makes it difficult to decide if and in what extent local treatment conditions have an impact on the permeabilization. Therefore, a kinetic model for the perforation of microalgae cells of the species Chlorella vulgaris was developed in the present work. The model describes the fraction of perforated cells as a function of the electric field strength, the temperature and the treatment time by using data which were obtained in a milliliter scale batchwise treatment chamber. Thereafter, the model was implemented in a CFD simulation of a pilot-scale continuous treatment chamber with colinear electrode arrangement. The numerical results were compared to experimental measurements of cell permeabilization in a similar continuous treatment chamber. The predicted values and the experimental data agree reasonably well what demonstrates the validity of the proposed model. Therefore, it can be applied to any possible treatment chamber geometry and can be used as a tool for scaling cell permeabilization of microalgae by means of PEF from lab to pilot scale. The present work provides the first contribution showing the applicability of kinetic modeling and numerical simulation for designing PEF processes for the purpose of biorefining microalgae biomass. This can help to develop new processes and to reduce the costs for the development of new treatment chamber designs.DFG, 414044773, Open Access Publizieren 2019 - 2020 / Technische Universität Berli
Characterization of fast-growing foams in bottling processes by endoscopic imaging and convolutional neural networks
Regardless of whether the occurrence of foams in industrial processes is desirable or not, the knowledge about the characteristics of their formation and morphology is crucial. This study addresses the measuring of characteristics in foam and the trailing bubbly liquid that result from air bubble entrainment by a plunging jet in the environment of industry-like bottling process es of non-carbonated beverages. Typically encountered during the bottling of fruit juices, this process configuration is characterized by very fast filling speeds with high dynamic system parameter changes. Especially in multiphase systems with a sensitive disperse phase like gas bubbles, the task of its measurement turns out to be difficult. The aim of the study is to develop and employ an image processing capability in real geometries under realistic industrial conditions, e.g. as opposed to a narrow measurement chamber. Therefore, a typically sized test bottle was only slightly modified to adapt an endoscopic measurement technique and to acquire image data in a minimally invasive way. Two convolutional neural networks (CNNs) were employed to analyze irregular non-overlapping bubbles and circular overlapping bubbles. CNNs provide a robust object recognition for varying image qualities and therefore can cover a broad range of process conditions at the cost of a time-consuming training process. The obtained single bubble and population measurements allow approximation, correlation and interpretation of the bubble size and shape distributions within the foam and in the bubbly liquid. The classification of the measured foam morphologies and the influence of operating conditions are presented. The applicability to the described test case as an industrial multiphase process reveals high potential for a huge field of operations for particle size and shape measurement by the introduced method
Development of a Continuous Pulsed Electric Field (PEF) Vortex-Flow Chamber for Improved Treatment Homogeneity Based on Hydrodynamic Optimization
Pulsed electric fields (PEF) treatment is an effective process for preservation of liquid products in food and biotechnology at reduced temperatures, by causing electroporation. It may contribute to increase retention of heat-labile constituents with similar or enhanced levels of microbial inactivation, compared to thermal processes. However, especially continuous PEF treatments suffer from inhomogeneous treatment conditions. Typically, electric field intensities are highest at the inner wall of the chamber, where the flow velocity of the treated product is lowest. Therefore, inhomogeneities of the electric field within the treatment chamber and associated inhomogeneous temperature fields emerge. For this reason, a specific treatment chamber was designed to obtain more homogeneous flow properties inside the treatment chamber and to reduce local temperature peaks, therefore increasing treatment homogeneity. This was accomplished by a divided inlet into the chamber, consequently generating a swirling flow (vortex). The influence of inlet angles on treatment homogeneity was studied (final values: radial angle α = 61°; axial angle β = 98°), using computational fluid dynamics (CFD). For the final design, the vorticity, i.e., the intensity of the fluid rotation, was the lowest of the investigated values in the first treatment zone (1002.55 1/s), but could be maintained for the longest distance, therefore providing an increased mixing and most homogeneous treatment conditions. The new design was experimentally compared to a conventional co-linear setup, taking into account inactivation efficacy of Microbacterium lacticum as well as retention of heat-sensitive alkaline phosphatase (ALP). Results showed an increase in M. lacticum inactivation (maximum Δlog of 1.8 at pH 7 and 1.1 at pH 4) by the vortex configuration and more homogeneous treatment conditions, as visible by the simulated temperature fields. Therefore, the new setup can contribute to optimize PEF treatment conditions and to further extend PEF applications to currently challenging products
Far Ultraviolet Spectroscopic Explorer Spectroscopy of Absorption and Emission Lines from the Narrow-Line Seyfert 1 Galaxy NGC 4051
We present three Far Ultraviolet Spectroscopic Explorer (FUSE) observations
of the Narrow-Line Seyfert 1 galaxy NGC4051. The most prominent features in the
far-ultraviolet (FUV) spectrum are the OVI emission and absorption lines and
the HI Lyman series absorption lines which are detected up to the Lyman edge.
We also identify weak emission from NIII, CIII, and HeII. The CIII line shows
absorption while none is detected in the NIII and HeII lines. In HI and CIII we
detect two main absorption systems at outflow velocities of -50+/-30 and
-240+/-40 km/s, as well as a possible third one at ~ -450 km/s. These systems
are consistent in velocity with the 10 absorption systems found previously in
CIV, NV, and SiIV, though the individual systems are blended together in the
FUV spectrum. We estimate column densities of the two main absorption systems
and find that the HI column density is lower for systems with larger outflow
velocity. We detect no flux or spectral variations of NGC4051 at FUV
wavelengths during three epochs spanning one year. This is consistent with the
optical light curve which shows no variations between the three epochs. It is
also consistent with the X-ray light curve which shows consistent flux levels
at the three epochs of the FUSE observations, although the X-ray light curve
shows strong variations on much shorter timescales.Comment: 9 pages, 7 figures (5 in color), emulateapj, accepted for publication
in The Astronomical Journa
Relativistic Broadening of Iron Emission Lines in a Sample of AGN
We present a uniform X-ray spectral analysis of eight type-1 active galactic
nuclei (AGN) that have been previously observed with relativistically broadened
iron emission lines. Utilizing data from the XMM-Newton European Photon Imaging
Camera (EPIC-pn) we carefully model the spectral continuum, taking complex
intrinsic absorption and emission into account. We then proceed to model the
broad Fe K feature in each source with two different accretion disk emission
line codes, as well as a self-consistent, ionized accretion disk spectrum
convolved with relativistic smearing from the inner disk. Comparing the
results, we show that relativistic blurring of the disk emission is required to
explain the spectrum in most sources, even when one models the full reflection
spectrum from the photoionized disk.Comment: 50 pages (preprint format), 24 figures. Accepted by Ap
The Black Hole Mass of NGC 4151: Comparison of Reverberation Mapping and Stellar Dynamical Measurements
We present a stellar dynamical estimate of the black hole (BH) mass in the
Seyfert 1 galaxy, NGC 4151. We analyze ground-based spectroscopy as well as
imaging data from the ground and space, and we construct 3-integral
axisymmetric models in order to constrain the BH mass and mass-to-light ratio.
The dynamical models depend on the assumed inclination of the kinematic
symmetry axis of the stellar bulge. In the case where the bulge is assumed to
be viewed edge-on, the kinematical data give only an upper limit to the mass of
the BH of ~4e7 M_sun (1 sigma). If the bulge kinematic axis is assumed to have
the same inclination as the symmetry axis of the large-scale galaxy disk (i.e.,
23 degrees relative to the line of sight), a best-fit dynamical mass between
4-5e7 M_sun is obtained. However, because of the poor quality of the fit when
the bulge is assumed to be inclined (as determined by the noisiness of the
chi^2 surface and its minimum value), and because we lack spectroscopic data
that clearly resolves the BH sphere of influence, we consider our measurements
to be tentative estimates of the dynamical BH mass. With this preliminary
result, NGC 4151 is now among the small sample of galaxies in which the BH mass
has been constrained from two independent techniques, and the mass values we
find for both bulge inclinations are in reasonable agreement with the recent
estimate from reverberation mapping (4.57[+0.57/-0.47]e7 M_sun) published by
Bentz et al.Comment: 20 pages, including 11 low-res figures. Accepted for publication in
ApJ. High resolution version available upon reques
High-Resolution X-ray and Ultraviolet Spectroscopy of the Complex Intrinsic Absorption in NGC 4051 with Chandra and HST
We present the results from simultaneous observations of the Narrow-Line
Seyfert 1 galaxy NGC 4051 with the Chandra High Energy Transmission Grating
Spectrometer and the HST Space Telescope Imaging Spectrograph. The X-ray
grating spectrum reveals absorption and emission lines from hydrogen-like and
helium-like ions of O, Ne, Mg and Si. We resolve two distinct X-ray absorption
systems: a high-velocity blueshifted system at -2340+/-130 km/s and a
low-velocity blueshifted system at -600+/-130 km/s. In the UV spectrum we
detect strong absorption, mainly from C IV, N V and Si IV, that is resolved
into as many as nine different intrinsic absorption systems with velocities
between -650 km/s and 30 km/s. Although the low-velocity X-ray absorption is
consistent in velocity with many of the UV absorption systems, the
high-velocity X-ray absorption seems to have no UV counterpart. In addition to
the absorption and emission lines, we also observe rapid X-ray variability and
a state of low X-ray flux during the last ~15 ks of the observation. NGC 4051
has a soft X-ray excess which we fit in both the high and low X-ray flux
states. The high-resolution X-ray spectrum directly reveals that the soft
excess is not composed of narrow emission lines and that it has significant
spectral curvature. A power-law model fails to fit it, while a blackbody
produces a nearly acceptable fit. We compare the observed spectral variability
with the results of previous studies of NGC 4051.Comment: 16 pages, 13 figures included, LaTeX emulateapj5.sty, accepted for
publication in The Astrophysical Journal (this version is the same as the
first version
The X-ray variability of the Seyfert~1 galaxy MCG-6-30-15 from long ASCA and RXTE observations
We present an analysis of the long RXTE observation of the Seyfert~1 galaxy
MCG-6-30-15, taken in July 1997. Our results show that the behaviour is
complicated. We find clear evidence from colour ratios and direct spectral
fitting that changes to the intrinsic photon index are taking place. Spectral
hardening is evident during periods of diminished intensity; in particular, a
general trend for harder spectra is seen in the period following the hardest
RXTE flare. Flux-correlated studies further show that the 3-10 keV photon index
steepens while that in the 10-20 keV band, flattens with flux. The largest
changes come from the spectral index below 10keV; however, changes in the
intrinsic power law slope, and reflection both contribute in varying degrees to
the overall spectral variability. We find that the iron line flux is consistent
with being constant over large time intervals on the order of days (although
the ASCA and RXTE spectra show that changes on shorter time
intervals of order < 10ks), and equivalent width which anticorrelates with the
continuum flux, and reflection fraction. Flux-correlated studies point at
possible ionization signatures, while detailed spectral analysis of short time
intervals surrounding flare events hint tentatively at observed spectral
responses to the flare. We present a simple model for partial ionization where
the bulk of the variability comes from within 6r_g. Temporal analysis further
provides evidence for possible time (< 1000s) and phase (phi~0.6 rad) lags.
Finally, we report an apparent break in the power density spectrum (~ 4-5 x
10^{-6}Hz) and a possible 33 hr period. Estimates for the mass of the black
hole in MCG-6-30-15 are discussed in the context of spectral and temporal
findings.Comment: 19 pages, 38 figures total (19 figure captions), accepted for
publication in MNRAS July 200
PTF10iya: A short-lived, luminous flare from the nuclear region of a star-forming galaxy
We present the discovery and characterisation of PTF10iya, a short-lived (dt
~ 10 d, with an optical decay rate of ~ 0.3 mag per d), luminous (M_g ~ -21
mag) transient source found by the Palomar Transient Factory. The
ultraviolet/optical spectral energy distribution is reasonably well fit by a
blackbody with T ~ 1-2 x 10^4 K and peak bolometric luminosity L_BB ~ 1-5 x
10^44 erg per s (depending on the details of the extinction correction). A
comparable amount of energy is radiated in the X-ray band that appears to
result from a distinct physical process. The location of PTF10iya is consistent
with the nucleus of a star-forming galaxy (z = 0.22405 +/- 0.00006) to within
350 mas (99.7 per cent confidence radius), or a projected distance of less than
1.2 kpc. At first glance, these properties appear reminiscent of the
characteristic "big blue bump" seen in the near-ultraviolet spectra of many
active galactic nuclei (AGNs). However, emission-line diagnostics of the host
galaxy, along with a historical light curve extending back to 2007, show no
evidence for AGN-like activity. We therefore consider whether the tidal
disruption of a star by an otherwise quiescent supermassive black hole may
account for our observations. Though with limited temporal information,
PTF10iya appears broadly consistent with the predictions for the early
"super-Eddington" phase of a solar-type star disrupted by a ~ 10^7 M_sun black
hole. Regardless of the precise physical origin of the accreting material, the
large luminosity and short duration suggest that otherwise quiescent galaxies
can transition extremely rapidly to radiate near the Eddington limit; many such
outbursts may have been missed by previous surveys lacking sufficient cadence.Comment: 18 pages, 8 figures; revised following referee's comment
Traces of past activity in the Galactic Centre
The Milky Way centre hosts a supermassive Black Hole (BH) with a mass of
~4*10^6 M_Sun. Sgr A*, its electromagnetic counterpart, currently appears as an
extremely weak source with a luminosity L~10^-9 L_Edd. The lowest known
Eddington ratio BH. However, it was not always so; traces of "glorious" active
periods can be found in the surrounding medium. We review here our current view
of the X-ray emission from the Galactic Center (GC) and its environment, and
the expected signatures (e.g. X-ray reflection) of a past flare. We discuss the
history of Sgr A*'s past activity and its impact on the surrounding medium. The
structure of the Central Molecular Zone (CMZ) has not changed significantly
since the last active phase of Sgr A*. This relic torus provides us with the
opportunity to image the structure of an AGN torus in exquisite detail.Comment: Invited refereed review. Chapter of the book: "Cosmic ray induced
phenomenology in star forming environments" (eds. Olaf Reimer and Diego F.
Torres
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